1. Field of the Invention
The present invention relates to a pattern forming method for use in the process of producing a semiconductor such as IC, in the production of a circuit board for liquid crystal, thermal head and the like, and in the lithography process of other photofabrications; a positive resist composition for multiple development used in the pattern forming method; a developer for negative development used in the pattern forming method; and a rinsing solution for negative development used in the pattern forming method. More specifically, the present invention relates to a pattern forming method suitable for exposure with an ArF exposure apparatus using a light source that emits far ultraviolet light at a wavelength of 300 nm or less or with an immersion-type projection exposure apparatus; a positive resist composition for multiple development used in the pattern forming method; a developer for negative development used in the pattern forming method; and a rinsing solution for negative development used in the pattern forming method.
2. Description of the Related Art
Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as a resist image forming method so as to compensate for sensitivity reduction incurred from light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area by exposure to generate an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the post-exposure baking (PEB), and removing the exposed area by alkali development.
Along with the finer fabrication of a semiconductor device, there is becoming shorter the wavelength of the exposure light source and higher the numerical aperture (high NA) of the projection lens, and an exposure machine using an ArF excimer laser having a wavelength of 193 nm as a light source has been so far developed. As commonly well known, these features can be expressed by the following formulae:(Resolving power)=k1·(λ/NA)(Focal depth)=±k2·λ/NA2 wherein λ is the wavelength of the exposure light source, NA is the numerical aperture of the projection lens, and k1 and k2 are coefficients related to the process.
A so-called immersion method of filling a high refractive-index liquid (hereinafter sometimes referred to as an “immersion liquid”) between the projection lens and the sample has been conventionally advocated as a technique of increasing the resolving power.
As for the “effect of immersion”, assuming that NA0=sin θ, the above-described resolving power and focal depth in the immersion can be expressed by the following formulae:(Resolving power)=k1·(λ0/n)/NA0 (Focal depth)=±k2·(λ0/n)/NA02 wherein λ0 is the wavelength of exposure light in air, n is the refractive index of the immersion liquid based on air, and θ is the convergence half-angle of beam.
That is, the effect of immersion is equal to use of an exposure wavelength of 1/n. In other words, in the case of a projection optical system with the same NA, the focal depth can be made n times larger by the immersion. This is effective for all pattern profiles and can be combined with a super-resolution technique under study at present, such as phase-shift method and modified illumination method.
A double exposure technology or a double patterning technology is being advocated as a technique for more enhancing the resolving power. This is to make small k1 in the above-described formula of resolving power and is positioned as a resolving power-increasing technique.
In conventional pattern formation of an electronic device such as semiconductor device, a mask or reticle pattern in a size of 4 to 5 times larger than the pattern intended to form is reduced and transferred on an exposure target such as wafer by using a reduction projection exposure apparatus.
With the progress to finer dimension, the conventional exposure system comes to encounter a problem that lights irradiated on adjacent patterns interfere each other to decrease the optical contrast. Therefore, in these techniques, a process of dividing the exposure mask design into two or more parts and synthesizing an image by independently exposing these masks is being employed. In these double exposure systems, it is necessary to divide the exposure mask design and again synthesize an image of the design on an exposure target (wafer), and division of the mask design needs to be devised so that the pattern on the reticle can be faithfully reproduced on the exposure target.
Studies of applying the effect of these double exposure systems to the transfer of a fine image pattern of a semiconductor device are introduced, for example, in JP-A-2006-156422 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
Also, the recent progress of double exposure technology is reported in SPIE Proc 5754, 1508 (2005), SPIE Proc 5377, 1315 (2004), SPIE Proc 61531K-1 (2006) and the like.
However, in these double exposure systems, the pattern formation needs to be performed in the vicinity of resolution limit of the resist and therefore, if the pattern formation is performed by merely applying the conventional resist composition to the conventional resist process, there arises a problem that sufficient exposure margin or focal depth cannot be obtained.
In other words, when the pattern forming process of coating a positive resist composition on a substrate and subjecting the resist film to exposure and development with an alkali developer described, for example, in JP-A-2001-109154 or the pattern forming process of coating a negative resist composition on a substrate and subjecting the resist film to exposure and development with an alkali developer described, for example, in JPA-2003-76019 is applied to a double exposure process, a sufficiently high resolving performance cannot be obtained.
As regards the developer for g-line, 1-line, KrF, ArF, EB or EUV lithography, an aqueous alkali developer of 2.38 mass % TMAH (tetramethylammonium hydroxide) is being used at present as a positive resist developer and a negative resist developer.
Other than the above-described developer, for example, JP-A-2001-215731 describes a positive resist developer containing an aliphatic linear ether-based solvent or aromatic ether-based solvent and a ketone-based solvent having a carbon number of 5 or more, which is used for developing a resist material containing a copolymer of a styrene-based monomer and an acryl-based monomer. Also, JP-A-2006-227174 describes a positive resist developer having at least two or more acetic acid groups, ketone groups, ether groups or phenyl groups and having a molecular weight of 150 or more, which is used for a resist material capable of dissolving in a solvent as a result of reduction in the molecular weight due to breakage of the polymer chain upon irradiation with radiation. JP-A-6-194847 describes a negative photoresist developer, where an aromatic compound having a carbon number of 6 to 12 or a mixed solvent containing 50 mass % or more of an aromatic compound having a carbon number of 6 to 12 is used as the developer for developing a negative photoresist mainly comprising a photosensitive polyhydroxy ether resin obtained by the reaction of a polyhydroxy ether resin and a diglycidyl (meth)acrylate.
Furthermore, JP-T-2002-525683 (the term “JP-T” as used herein means a “published Japanese translation of a PCT patent application”) describes a positive resist developer for developing a resist composition containing a specific fluorine-containing resin, where the positive resist developer contains an organic solvent, particularly, a halogenated organic solvent, and JP-T-2006-518779 describes a negative resist developer for developing a negative photoresist composition containing a specific polycyclic olefin polymer, where the negative resist developer contains one or more solvents selected from the group consisting of propylene glycol methyl ether acetate, cyclohexanone, butyrolactate and ethyl lactate.
JP-A-2000-199953 discloses a method to improve the resolution double with an ordinary positive resist.
However, the above-described combinations of a resist compositions and a developer merely provide a system of performing pattern formation by combining a specific resist composition with either a positive developer or a negative developer.
That is, as shown in FIG. 1, in the case of a positive system (a combination of a resist composition and a positive developer), a material system of performing pattern formation by selectively dissolving and removing the region having a strong light irradiation intensity out of the optical aerial image (light intensity distribution) is merely provided. On the other hand, as for the combination of a negative system (a resist composition and a negative developer), a material system of performing pattern formation by selectively dissolving and removing the region having a weak light irradiation intensity is merely provided.